(1) Field of the Invention
The present invention relates to the field of aircraft, and in particular to the field of rotorcraft, and it relates more particularly to command systems of transmissions that are actuated by a human for controlling the flight directions of an aircraft, and in particular in pitching and in roll. The invention relates more specifically to control sticks for controlling the flight directions of an aircraft, and in particular for changing the angle of incidence of the blades of a rotor equipping a rotorcraft. The invention relates, in particular, to a control stick for mechanically transmitting commands that is of structure axially short and suitable for being incorporated in the armrest of a pilot's seat.
(2) Description of Related Art
Rotorcraft are commonly equipped with manually operated control systems for enabling a pilot to control the rotorcraft. Among such control systems, a cyclic control lever enables the pilot to change the angle of incidence of the blades so as to control the rotorcraft on the basis of selective flight commands, respectively for pitching control and for roll control. The control lever is hinged to a frame, e.g. being arranged as a box or the like, while being mounted to tilt in at least two control directions that are assigned to respective flight commands. The control lever is in hinged engagement with the frame at a distal one of its ends, and is provided at its proximal other end with a grip that can be taken hold of by the pilot. The proximal end is the end of the control lever that can be manipulated by the pilot, the distal end being the end of the control lever that is opposite from the proximal end. As soon as the control lever is tilted in either of the control directions, a corresponding command transmission member is activated to bring into use a remote power-assisted member, in particular a hydraulic servo-control actuator, that is assigned to corresponding pitching or roll flight control. The transmission member may be of the mechanical type, by being arranged as a rod, as a link, as a ball-bearing sheath, as a cable, or as an analogous remote mechanical transmission member, or else said transmission member may be of the electrical type by being arranged as a contactor connected to the remote power-assisted member via a wire connection.
Among cyclic control levers, long cyclic columns are known that tend to be reserved for transmitting commands mechanically, and short cyclic sticks are known that tend to be reserved for transmitting commands electrically. By way of indication, the length of a long cyclic column is about three to four times the length of a short cyclic stick. A long cyclic column is hinged in front of the seat and offers the advantage of transmitting commands mechanically, which is less costly than transmitting commands electrically.
A cyclic column has a lever arm that is considerable, thereby facilitating mechanical transmission of commands, and making manipulation easy for the pilot. Pilots can use their entire arms for operating the cyclic column with appropriate force, and can feel directly the resistance forces opposed by the remote power-assisted members against being operated.
A cyclic stick, of small size, can be mounted in the armrest of a pilot's seat, so as to make control comfortable for the pilot sitting in the seat, with improved visibility and improved overall ergonomics for the cockpit, by releasing the space extending in front of the pilot sitting in the seat. The cyclic stick is easy to manipulate since it can be tilted effortlessly through small amplitudes and effortlessly by wrist actions of the pilot, with this being made possible by using electrical-type transmission means and by implementing an electromechanical force-simulation device that is servo-controlled to the remote power-assisted members so as to reproduce the resistance forces they oppose to being operated.
Ideally, a good compromise could be obtained by using a short cyclic stick suitable for incorporating in the armrest, and by equipping the stick with transmission members of the mechanical type. In order to mitigate the insufficient lever arm of the cyclic stick, a force-developing assistance device may be interposed in the transmission system between the cyclic stick and the remote power-assisted member. Unfortunately, that solution is not fully satisfactory as it stands, and needs improving. It is found that, in the event of malfunction of the assistance devices, the cyclic stick becomes difficult to use.
For information about a technological environment close to the present invention, reference can be made, for example, to Documents EP 0 844 171 (AEROSPATIALE) and US 2008/0272243 (DECKER W. E.) that describe flight control mechanisms for controlling flight of an aircraft that implement control sticks.
The teaching from the following documents is also known: EP 1 218 240 (BELL HELICOPTER TEXTRON INC) discloses the use of a device making it possible to modulate the relationships governing forces felt by the pilot on the pilot's control member. U.S. Pat. No. 4,961,548 (ROCKWELL INT CORP) discloses a console for supporting a control stick, which console is mounted telescopically on the floor of an aircraft. Document U.S. Pat. No. 3,209,612 (HAMBURGER FLUGZEUGBRAU GMBH) describes a column that is mounted to the floor of an aircraft so as to move longitudinally in order to procure flight control on the basis of its movement.
Document US 2010/0123045 presents a control mechanism provided with a column cooperating with a trim actuator.
Document GB 279 206 discloses a control mechanism for protecting a pilot from control means in the event of an accident.